1. Field
One or more embodiments of the present invention relate to the field of electronic circuits and systems and more particularly to voltage controlled oscillator circuits.
2. Discussion of Related Art
A voltage controlled oscillator (VCO) is a circuit that receives a control voltage and generates an output signal with a frequency that is a function of the control voltage. Fluctuations in the output signal of the VCO results in phase noise that is undesirable for the system.
In high linearity radio receivers, reciprocal mixing affects the signal-to-noise ratio (SNR) and degrades the sensitivity of the receiver. Reciprocal mixing may occur when the phase noise over 50 MHz away mixes with blockers, which are undesired large signals from external sources. These blockers degrade the SNR and as a result limit the sensitivity of the receiver.
Typically, far-out phase noise in a VCO can be reduced by doubling the DC power/current while lowering the load resistance. As a result, the SNR improves by 3 dB for each doubling of power under ideal conditions. However, this increases the power dissipation of the VCO.